Falls are a leading cause of morbidity and mortality among older adults. Although gait and mobility are generally considered over-learned and automatic functions, recent findings highlight the potential importance of cognitive function in fall risk and gait variability. Preliminary work suggests that specifically higher-level cognitive function influences gait variability and fall risk, but the relationships between cognitive function and gait variability have not been well-studied. For example, it is not clear if or why idiopathic elderly fallers increase stride-to-stride variability when they perform a secondary task while walking. Two studies of cognitive function, gait variability, and fall risk will be performed. These studies of multiple aspects of cognitive function and gait, especially under "dual tasking" conditions, should demonstrate that gait, in particular gait variability, is related to and may rely on executive function and attention. Specifically, we will test the following hypotheses: 1) Executive function and attention influence gait variability and fall risk in older adult, "idiopathic" fallers. Using computerized neuropsychological testing, we aim to identify, for the first time, the specific components of cognitive function that modulate gait variability, fall risk, and dual-tasking gait abilities among community living older adults (fallers and non-fallers) and healthy young adults. 2) Changes over time in gait variability parallel changes in cognitive function. A three-year prospective study of community living older adults will be performed to identify which changes in cognitive function over time are associated with changes in gait and fall risk, and to determine whether the assessment of cognitive function and gait variability enhances the prospective identification of future fallers. This prospective study will allow us to document the natural history of two physiologic systems that commonly decline in older adults, to answer key questions regarding the nature of gait and fall risk in older adults and their dependence on cognitive function, and to set the stage for for new ways of treating gait disturbances and reducing fall risk.